Photobacterium profundum strain SS9 is a piezophile that optimally
grows at 28 MPa and 9 °C. It contains EPA at a proportion of 11% when
cultured under the condition. The lack of EPA does not affect the growth
of this bacterium under high pressure and low temperature, whereas
the lack of cis-vaccenic acid (C18:1) significantly diminishes growth
under the same conditions [39]. Accordingly, monounsaturated fatty
acids but not PUFAs are required for growth of P. profundum under high
pressure and low temperature. In cold-adapted bacterium Shewanella
livingstonensis Ac10 isolated fromAntarctic seawater, EPA plays a specific
role in fulfilling appropriate cell division at low temperatures [43]. However,
EPA may not be required for membrane fluidity, based on the finding
that the loss of EPA does not affect the diffusion rate of a small
lipophilicmolecule, pyrene, in the membrane. In Shewanella piezotolerans
WP3 isolated from the western Pacific Ocean, the loss of EPA results in
growth defects at low temperature (4 °C, 0.1 MPa) and high pressure
(20 °C, 20 MPa), indicating the requirement of EPA for growth under these conditions. Shewanella violacea strain DSS12 is a deep-sea bacterium
isolated from the Ryukyu Trench at a depth of 5110 m and exhibits
piezophily with optimal growth at 30 MPa and 8 °C [44]. In this bacterium,
EPA also plays a role in appropriate cell division under high pressure
[45].